1498 JOURNAL OF HYDROMETEOROLOGY VOLUME 12 Snow Cover and Spring Flood Flow in the Northern Part of Western Siberia (the Poluy, Nadym, Pur, and Taz Rivers) ,1,# ,# ,1,& ,@ E. A. ZAKHAROVA,* A. V. KOURAEV,* S. BIANCAMARIA,* M. V. KOLMAKOVA,* ,& @ @ N. M. MOGNARD,* V. A. ZEMTSOV, S. N. KIRPOTIN, AND B. DECHARME** * UPS (OMP-PCA), LEGOS, Universite´ de Toulouse, Toulouse, France 1 CNRS, LEGOS, Toulouse, France # St. Petersburg Branch, State Oceanography Institute, St. Petersburg, Russia @ Tomsk State University, Tomsk, Russia & CNES, LEGOS, Toulouse, France ** GAME–Centre National de Recherche Me´te´orologique, Toulouse, France (Manuscript received 11 February 2011, in final form 6 May 2011) ABSTRACT The paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the re- distribution of river runoff for the northern (Arctic) part of the western Siberian Plain (the rivers Poluy, Nadym, Pur, and Taz). In this region, the presence of wetlands and thermokarst lakes significantly influences the seasonal redistribution of river discharge. First the study region is described, and the snow regime from in situ observations at the Tarko-Sale meteorological station is analyzed. As Special Sensor Microwave Imager (SSM/I) estimates of snow depth for this region are lower than in situ observations, a correction of the SSM/I snow depth estimates is done using snow parameters measured on the snow transect near the meteorological station Tarko-Sale for 1991–96. This reestimated snow depth is then used to assess the volume of water stored every winter on the watersheds for 1989–2006. This snow product is compared with the spring flood streamflow estimated from in situ observations, and the regional relationship between the snow water storage and flood flow is constructed. The proportion of meltwater that does not reach the main rivers and is thus evaporated or stored by the wetlands is estimated to be on average 30% (varying from 0% to 74%). We observe an increasing trend of this value from 20%–30% in the early 1990s to 50%–60% in the mid-2000s. This increase could be attributed to several factors such as increased air temperature (leading to increased evaporation, changes in vegetation cover, and active layer depth) and also to human activity. 1. Introduction and human activity on the functioning of boreal water- sheds, we need to estimate and quantify the role and High-latitude terrestrial ecosystems respond to global contribution of various components of the water budget. climate changes through exchange of water, energy, and One of the key components of the water budget is the gases with the atmosphere and through freshwater input snow cover. Its contribution to the river outflow and its to the Arctic Ocean. Climatic changes are already af- seasonal and interannual variability is very dynamic, and fecting boreal river systems through rising air tempera- changes in snowmelt runoff will be one of the most pro- ture and precipitation (Zakharova et al. 2009b), thawing nounced hydrologic responses to climate change. The of permafrost (Zhang et al. 2003), disappearing lakes snow depth (SD) and snow water equivalent (SWE) are (Smith et al. 2005), and increase in river runoff (Grippa important for a number of applications and tools, in- et al. 2007; De´ry et al. 2009; Yang et al. 2003). To improve cluding flood estimation and prediction and hydrological our understanding of the processes and feedbacks in- modeling. The existing network of terrestrial observa- volved, as well as the potential impact of climate variability tions of snow cover parameters is sparse and often not able to represent well the processes on large and mid- sized watersheds (Shiklomanov et al. 2002). In this re- Corresponding author address: A. V. Kouraev, UPS (OMP-PCA), LEGOS, Universite´ de Toulouse, 14 Av. Edouard Belin, F-31400 spect a very promising solution is to combine in situ data Toulouse, France. with satellite microwave remote sensing techniques. Sat- E-mail: [email protected] ellite observations of spatial and temporal distribution DOI: 10.1175/JHM-D-11-017.1 Ó 2011 American Meteorological Society Unauthenticated | Downloaded 10/02/21 04:26 AM UTC DECEMBER 2011 Z A K H A R O V A E T A L . 1499 FIG. 1. Overview map of the northern western Siberia, showing watersheds and main streams for the Poluy, Nadym, Pur, and Taz River systems, as well as permafrost types (shades of gray; type labels are on map) after Kondratyev and Kudryavtsev (1981) (only types within the PNPT watershed are shown). of various snowpack parameters, once calibrated with The relationship between river discharge and snow- the in situ data, provide continuous, reliable, regular, and melt water for the Ob’ watershed has been addressed weather-independent data over large regions. in several publications (Burakov 1978; Yang et al. 2003; Western Siberia is a large flat region located between Berezovskaya et al. 2004; Ye et al. 2004; Grippa et al. the Ural Mountains and the middle Siberian Highlands. 2005, 2007; Papa et al. 2007). These authors have ana- Most of its territory comprises the watershed of the Ob’ lyzed the relationship between the Ob’ River discharge River (almost 3 million km2); while its northern part (measured at the outlet station Salekhard) and various contains the rivers Nadym, Pur, and Taz, as well as environmental parameters from in situ observation net- western tributaries of the Yenisey River (Fig. 1). The work and remote sensing observations. These parame- total annual runoff from western and eastern Siberia ters include snow depth, snow extent, snowmelt timing, to the Kara Sea is 1250 km3 yr21. This is the maximal inundated zones extent, air temperature, and precipita- freshwater input among all other Arctic seas, and it tion. They stress the importance of evapotranspiration dramatically affects the hydrology, hydrochemistry, and (ET) in the Ob’ River watershed that is related to var- hydrobiology of the Arctic Ocean. ious factors (high percentage of ponds and wetlands, The presence of wetlands and numerous lakes in west- vegetation conditions, lower spatial extent of permafrost, ern Siberia results in a very high rate of evaporation— etc.). higher than for any other large Siberian watershed In this work we look at the northern part of the (Sokolov 1952). These natural objects also act as a western Siberian Plain [the rivers Poluy, Nadym, Pur, temporary storage of water after the spring snowmelt, and Taz (PNPT)]. Compared to the large watersheds of gradually releasing water in summer. These two factors rivers such as the Ob’ and Yenisey, which span at least significantly influence seasonal redistribution of river two different vegetation and climatic zones, PNPT rivers discharge. can be considered a relatively homogeneous region for Unauthenticated | Downloaded 10/02/21 04:26 AM UTC 1500 JOURNAL OF HYDROMETEOROLOGY VOLUME 12 their natural conditions, the influence of permafrost, and spatial variability of snow grain size derived from wetland coverage, and topography. the estimation of the thermal gradient in the snowpack By using values with high temporal resolution (such as (Mognard and Josberger 2002). We use this relationship daily values of discharge and meteorological parame- to assess the volume of water stored every winter on the ters) we aim at estimating the influence of the wetlands watersheds and compare it with the spring meltwater on the volume of snowmelt water and thus the seasonal flood volume for the four rivers (section 3). We quantify distribution of PNPT rivers discharge. This is a contin- the part of meltwater that does not reach the main rivers uation of previous work (Zakharova et al. 2009a) where and is thus evaporated or stored by the wetlands. We we have estimated annual input from spring snowmelt, analyze its temporal variability and put it in the context base flow, and interflow–overland flow by a quantifica- of the changes in surface properties due to climate tion of river runoff using a graphical hydrograph sepa- warming and human activity (section 4). ration approach (see section 4a). In the previous study we have verified the consistency 2. Study area of snow estimates from various datasets [from in situ stake observations of snow accumulation at Oktyabr’skaya The Ob’ and Yenisey have extensive and complicated station, National Centers for Environmental Prediction river systems that span large watersheds located in vari- (NCEP) reanalysis, and Special Sensor Microwave Im- ous climatic zones (from steppes to tundra) and thus have ager (SSM/I)] for establishing the relationship with the different natural and hydrological regimes for their vari- volume of spring meltwater. We have found that among ous parts. Smaller rivers in the northern part of western the datasets tested, the SSM/I estimates retrieved by the Siberia—the PNPT rivers (Fig. 1)—are characterized by dynamic algorithm (Grippa et al. 2004, 2005; Biancamaria more homogeneous natural conditions compared to the et al. 2008) better explain the interannual variability of Ob’ and Yenisey Rivers. Here we refer to the fact that the spring flood river output. Compared to stations, the PNPT rivers share similar climatic and geomorphological satellite snow product accounts for the spatial distribu- conditions: the same atmospheric circulation, frozen tion of snow cover over the watershed. It also takes into postglacial sediments, presence of continuous or discon- account temporal transformation of snow (grain size tinuous permafrost, flat bog plateaus, and sparse forest- change, sublimation, and wind redistribution) as com- tundra vegetation. This makes them a good proxy of pared to the reanalysis dataset, where snow is usually climate variability of the Arctic part of western Siberia. calculated as precipitation during the winter, and which Originating on the northern slopes of the Sibirskiye is based on data from a network of meteorological sta- Uvaly hills (altitude ranging from 170–200 m to 230– tions that are rather sparse in the Arctic region.